DEAR READER: Your question reminded me of something that happened many years ago. A new patient came to my office. She told me that a colleague of mine had been her doctor, but she had stopped seeing him because “he didn’t know what he was talking about.”

When I asked her to explain, she said that she had been weak and had almost fainted several times. At other times, her heart suddenly seemed to be beating too fast. So she saw her doctor. “He told me it was a sinus problem. How could my sinuses make me faint, or make my heart beat too fast?” she asked. So I told her what I’m about to tell you.

Sick sinus syndrome has nothing to do with your sinuses — the ones that get congested when you have a cold, or maybe from allergies. It is a heart condition, caused by the malfunctioning of a part of the heart called the “sinus node,” or the “sinoatrial node.” This small area of the heart keeps your heart rhythm normal or regular.

Each time your heart beats, a tiny electrical current triggers the heart muscle to contract. The stimulus is sent by the sinus node. This cluster of cells in the upper right portion of your heart acts as your body’s natural pacemaker.(I’ve put an illustration of the sinus node on my website, AskDoctorK.com.)

The electrical waves travel through the upper chambers of the heart (the atria). They then pause briefly in the atrioventricular (AV) node in the middle of the heart. The waves continue through specialized electrical connections in the lower heart chambers (the ventricles). This produces a nice rhythmic contraction of the heart muscle.

My colleague Dr. Patrick Ellinor is a cardiologist and arrhythmia specialist at Harvard-affiliated Massachusetts General Hospital. He explains that sick sinus syndrome can take many forms. The sinus node may fail to send out signals quickly enough, for example. As a result, your heart cannot beat fast enough to supply your body with fresh blood and oxygen. That’s why my patient was feeling weak and nearly fainting.

Or, a malfunctioning sinus node may shut down completely for five or six seconds. During that time, electrical activity stops and your heartbeat is put on pause. If that happens, you will most likely pass out. In another form of sick sinus syndrome, the heart rate alternates between a pace that is too fast and one that is too slow. That’s what was happening with my patient.

Sick sinus syndrome is more common in people in their 70s and 80s. Most cases result from age-related changes in the heart muscle that disrupt the heart’s electrical system. Certain medications used to treat other heart conditions can also increase risk.

The standard treatment is placement of an artificial pacemaker to regulate the heartbeat electronically. This requires minor surgery. But a pacemaker is a safe and effective option for keeping your heart beating on track.